To attain an accurate patient diagnosis, a medical radiologist typically relies upon a visual study of silver images in photographic elements. Image study usually occurs with the element mounted on a light box, a white translucent illumination source. Silver halide photographic elements can be exposed to X-radiation alone to produce viewable silver images. A more efficient approach, which greatly reduces X-radiation exposures, is to employ an intensifying screen in combination with the radiographic element. The intensifying screen absorbs X-radiation and emits longer wavelength electromagnetic radiation which silver halide emulsions more readily absorb. Another technique for reducing patient exposure is to coat two silver halide emulsion layers on opposite sides of the film support to form a "double coated" radiographic element. Diagnostic needs can be satisfied at the lowest patient X-radiation exposure levels by employing a double coated radiographic element in combination with a pair of intensifying screens. However, alternatives are now available to the radiologist for capturing the X-radiation image. For example, the X-radiation image can be captured in a storage phosphor screen. By subsequently scanning the exposed storage phosphor screen with stimulating radiation, an emission profile can be read out and sent to a computer where it is stored. Such an imaging approach is described in Luckey U.S. Pat. No. Re. 31,847 and DeBoer et al. U.S. Pat. No. 4,733,090.
To provide the radiologist with a viewable image that can be studied, the stored image information can be used as recorded or with computer enhancement, to expose a diagnostic photographic film, often using a modulated light emitting diode or He-Ne laser source emitting in the red or near infrared region of the electromagnetic spectrum as the exposure source. After exposure, the diagnostic photographic film is photographically developed to provide a silver image for examination. In a typical procedure, such a diagnostic photographic film is run through a processing cycle, usually a so-called rapid-access process in which processing is completed in 90 seconds or less, which is the same as the processing cycle used for processing diagnostic photographic film that is directly exposed to X-radiation. The same rapid-access process is used by the radiologist for efficiency of effort. Also, such rapid-access processing is capable of providing comparable viewable silver images in diagnostic photographic films when such images are provided by direct exposure to X-radiation or by alternative exposure techniques such as where the image is provided by scanning a storage phosphor screen. Furthermore, since a patient being examined cannot be released until successful recording of the silver images needed for diagnosis has been confirmed, the diagnostic photographic films are normally constructed to provide rapid-access processing.
A photographic element that can be used as a diagnostic film without direct exposure to X-radiation in the manner described hereinbefore, frequently comprises at least one emulsion layer containing radiation sensitive silver bromide or silver bromoiodide fine grains. Such elements have good speed and provide silver images exhibiting excellent definition of the type required for examination by a radiologist. Unfortunately, such silver images can exhibit a warm tone, for example, a yellowish, greenish or brown hue when the elements are viewed by transmitted light. For a skilled diagnostician, such warm tone images are an obstacle to accurate diagnosis. A neutrally black or colder tone image is desired.
U.S. Pat. No. 4,728,601 describes the use of certain 2-alkylthio-4-hydroxy-1,3,3a,7-tetraazaindenes to modify silver image tone in a photographic element and impart a neutral tone to a developed silver image formed upon exposure and processing of the element. Such image toning materials comprise a single sulfur atom in an alkylthio substituent and have the following formula: ##STR2## wherein R.sub.1 is alkyl containing 6 to 11 carbon atoms or is a ring system and the groups R.sub.2 and R.sub.3 are each individually hydrogen or alkyl containing 1 to 4 carbon atoms.
The above azole compounds are shown to be useful in an element comprising a gelatin fine grain silver chlorobromide emulsion containing 55 mole percent silver chloride and 45 mole percent silver bromide. U.S. Pat. No. 4,728,601 also alleges that such compounds are useful toning materials in photographic silver halide emulsions of any halide composition, but no data is presented in support of this allegation. Furthermore, it has been our experience, as demonstrated by Examples that follow, that monothiaalkyl substituted compounds of the type described in U.S. Pat. No. 4,728,601 are not effective for modifying the tone of a silver image formed from fine grain radiation sensitive silver bromide or silver bromoiodide emulsions.
U.S. Pat. Nos. 4,720,447 and 4,859,565 may, upon superficial examination, appear to be of some interest with respect to the present invention since these patents describe the use of heterocyclic azole compounds as density- and/or tone controlling compounds. However, these patents simply describe the use of such compounds in a photographic silver complex diffusion transfer reversal process (often simply referred to as a DTR process) wherein a silver image is formed in a non-radiation sensitive layer from a soluble silver salt. There is no suggestion that such compounds would have any effect in modifying the tone of a silver image formed from a fine grain radiation sensitive silver bromide or silver bromoiodide emulsion of the type used in the present invention. Furthermore, as demonstrated in the following Examples, U.S. Pat. Nos. 4,720,447 and 4,859,565 describe the use of a broad class of heterocyclic azole compounds that include many compounds that are taught to be effective for patentees' purposes, but would not be useful in the practice of this invention. For example, a large number of the heterocyclic azole compounds described in the aforementioned patents do not contain multiple sulfur atoms in an aliphatic substituent on an azole ring which is an essential feature of this invention. It is significant to note that for patentees' purposes, no distinction is made between heterocyclic azoles which contain no thiaalkyl substituents, those that contain only a single sulfur atom in a thiaalkyl substituent and those that contain multiple sulfur atoms in a thiaalkyl substituent. Accordingly, it is evident that U.S. Pat. Nos. 4,720,447 and 4,859,565 are not pertinent to the present invention which pertains to the use of a specific class of heterocyclic azoles to modify the tone of a silver image formed from a photographic element comprising an emulsion layer containing fine grains of radiation sensitive silver bromide or silver bromoiodide.
In the previous description, emphasis has been placed on the advantages of modifying the tone of a silver image formed from a diagnostic photographic film. However, it is well known in the art that photographic elements used for other purposes, e.g. in the field of graphic arts, can also benefit from such tone modification. Accordingly, this invention is specifically contemplated for use with such elements, as will be described in greater detail hereinafter.
In light of the previous discussion, it is obvious that it would be very desirable to have a photographic element, particularly one useful as a diagnostic photographic film, which would provide high definition silver images having a satisfactory tone. Likewise, it would be desirable to have such a photographic element with the capability of being processed using black and white processing procedures, especially conventional rapid-access X-ray processing techniques. This invention provides such a photographic element and a means for obtaining a neutral tone high definition silver image.